The present invention relates to electromagnetic transformers.
Electromagnetic transformers have been used in a wide variety of applications. Such applications, for example, include either stepping up or stepping down voltages and/or currents, for isolating high-voltage circuits from low-voltage circuits, for isolating circuits operating at one frequency from circuits operating at a different frequency, or for combining signals in any particularly-desired fashion. Normally, such transformers have an air core or they have a ferromagnetic core if it is desired to provide a high permeability path for the flux which passes through the windings of the transformer associated with such core. A ferromagnetic core provides a high degree of magnetic coupling between the windings and supports a larger amount of flux than is possible in an air core.
Multiple transformers can often be used to accomplish together what would otherwise be done by a single transformer such as when the amount of power to be handled by the transformer is so large that it is either impossible or impractical to use a single transformer. Another application for multiple winding transformers is in three-phase power systems. A three-phase power system typically produces three sinusoidal voltage sources where the voltages are equal in magnitude and frequency, but separated by predetermined phase shifts. The advantages of multiphase power systems include both more efficient conversion of electromechanical energy and savings in the transmission of the three-phase energy. Although early multiphase systems were for the most part two-phase, three-phase systems are the most commonly used multiphase system currently.
Because a three-phase transformer offers more efficient use of core materials as compared to three single-phase transformers which handles the same amount of apparent power, three-phase power systems typical]y rely upon single three-phase transformers. There are several possible known ways of combining cores of three transformers in order to obtain a single three-phase transformer. For example, a core-type three-phase transformer is essentially three single-phase core-type transformers whose magnetic circuits are wye connected. A core-type three-phase transformer typically has three columns of electromagnetic material with their ends joined by two corresponding rows of electromagnetic material. Each column carries a primary winding and a secondary winding for a respective phase of the three-phase system. A shell-type transformer, on the other hand, consists of a rectangularly-shaped electromagnetic core having three sets of holes, two holes for each set, distributed along the length of the core. Primary and secondary windings for each phase of the three-phase transformer are wound around the corresponding legs formed by the sets of holes. This transformer also offers some savings in core material. There are, of course, other types of core structures known in the art.
Also, three-phase transformers often rely principally upon a stationary, although oscillating, field for the transformation of voltage and transfer of energy. However, there have been known induction transformers which rely upon rotating fields for such transformation of voltage and transfer of energy.
Furthermore, it has been known to use three-phase transformers for the summation of voltages produced by multiple voltage sources. However, these summing transformer designs have relied upon stationary fields for the transformation of voltage and transfer of energy. These designs do not make efficient use of core iron and winding copper and, as a result, performance optimization is limited. Also, inefficient use of the core iron and winding copper causes an increase in bulk and/or weight with a resulting decrease in transformer efficiency.